The present invention relates to the field of removal of photoresist and residue from a substrate. More particularly, the present invention relates to the field of removal of photoresist and residue from a substrate using supercritical carbon dioxide.
Semiconductor fabrication uses photoresist in ion implantation, etching, and other processing steps. In the ion implantation steps, the photoresist masks areas of a semiconductor substrate that are not implanted with a dopant. In the etching steps, the photoresist masks areas of the semiconductor substrate that are not etched. Examples of the other processing steps include using the photoresist as a blanket protective coating of a processed wafer or the blanket protective coating of a MEMS (micro electro-mechanical system) device.
Following the ion implantation steps, the photoresist exhibits a hard outer crust covering a jelly-like core. The hard outer crust leads to difficulties in a photoresist removal.
Following the etching steps, remaining photoresist exhibits a hardened character that leads to difficulties in the photoresist removal. Following the etching steps, photorcsist residue mixed with etch residue coats sidewalls of etch features. Depending on a type of etching step and material etched, the photoresist residue mixed with the etch residue presents a challenging removal problem since the photoresist residue mixed with the etch residue often strongly bond to the sidewalls of the etch features.
Typically, in the prior art, the photoresist and the photoresist residue are removed by plasma ashing in an O2 plasma followed by stripping in a stripper bath.
FIG. 1 illustrates an n-p-n FET (field effect transistor) structure 10 subsequent to an ion implantation and prior to a photoresist removal. The n-p-n FET structure 10 includes a source region 12, a gate region 14, and a drain region 16 with isolation trenches 18 separating the n-p-n FET structure 10 from adjacent electronic devices. A first photoresist 20 masks all but the source and drain regions, 12 and 16. In the ion implantation, a high energy ion source implanted an n-dopant into the source and drain regions, 12 and 16. The high energy ion source also exposed the first photoresist 20 to the n-dopant which creates a hard crust on an upper surface 22 of the first photoresist 20. In the prior art, the first photoresist 20 is removed by the plasma ashing and the stripper bath of the prior art.
FIG. 2 illustrates a first via structure 30 of the prior art subsequent to an RIE (reactive ion etching) etch and prior to a photoresist and residue removal. The first via structure 30 includes a via 32 which is etched into a first SiO2 layer 34 to a first TiN layer 36. In the first via structure 30, the via 32 stops at the first TiN layer 36 because the first TiN layer 36 provides an etch stop for the RIE etch of the first SiO2 layer 34. Etching through the first TiN layer 36 complicates the RIE etch by requiring an additional etch chemistry for the first TiN layer 36; so for this particular etch, the TiN layer 36 is not etched. The first TiN layer 36 lies on a first Al layer 38, which lies on a first Ti layer 40. A first residue, which comprises photoresist residue 42 mixed with SiO2 etch residue 44, coats sidewalls 46 of the via 32. Second photoresist 48 remains on an exposed surface 50 of the first SiO2 layer 34. In the prior art, the second photoresist 48, the photoresist residue 42, and the SiO2 etch residue 44 are removed using the plasma ashing and the stripper bath of the prior art.
Note that specific layer materials and specific structure described relative to the first via structure 30, and to other thin film structures discussed herein, are illustrative. Many other layer materials and other structures are commonly employed in semiconductor fabrication.
FIG. 3 illustrates a second via structure 60 of the prior art subsequent to the RIE etch and prior to the photoresist and residue removal. The second via structure 60 includes a second via 62 which is etched through the first SiO2 layer 34 and the first TiN layer 36 to the first Al layer 38. By etching through the first TiN layer 36, a device performance is improved because a contact resistance with the first Al layer 38 is lower than the contact resistance with the first TiN layer 36. The second via structure 60 also includes the first Ti layer 40. The first residue, which comprises the photoresist residue 42 mixed with the SiO2 etch residue 44, coats second sidewalls 64 of the second via 62. A second residue, which comprises the photoresist residue 42 mixed with TiN etch residue 66, coats the first residue. The second photoresist 48 remains on the exposed surface 50 of the first SiO2 layer 34. In the prior art, the second photoresist 48, the photoresist residue 42, the SiO2 etch residue 44, and the TiN etch residue 66 are removed using the plasma ashing and the stripper bath of the prior art.
Note that the first residue (FIGS. 2 and 3) and the second residue (FIG. 3) are worst case scenarios. Depending upon a specific etch process, the first residue or the second residue might not be present.
FIG. 4 illustrates a metal line structure 70 subsequent to a metal RIE etch and prior to a residue removal. The metal line structure 70 includes a second TiN layer 72 on a second Al layer 74 which is on a second Ti layer 76. The second TiN layer 72, the second Al layer 74, and the second Ti layer 76 form a metal line. The second Ti layer 76 contacts a W via 78, which in turn contacts the first Al layer 38. The W via 78 is separated from the first SiO2 layer 34 by a sidewall barrier 80. A third residue, which comprises a halogen residue 82 mixed with metal etch residue 84, lies on the exposed surface 50 of the first SiO2 layer 34. The third residue, which comprises the halogen residue 82 and the metal etch residue 84, also lies on a second exposed surface 86 of the second TiN layer 72. A fourth residue, which comprises a combination of the photoresist residue 42 mixed with metal etch residue 84, coats sides 88 of the metal line. Skirts 90 of the fourth residue extend above the second exposed surface 86 of the second TiN layer 72. In the prior art, the photoresist residue 42, the halogen residue 82, and the metal etch residue 84 are removed using the plasma ashing and the stripper bath of the prior art.
FIG. 5 illustrates a dual damascene structure 100 of the prior art subsequent to a dual damascene RIE etch and prior to the photoresist and photoresist residue removal. The dual damascene structure 100 includes a dual damascene line 102 formed above a dual damascene via 104. The dual damascene line 102 is etched through a second SiO2 layer 106 and a first SiN layer 108. The dual damascene via 104 is etched through a third SiO2 layer 110 and a second SiN layer 112. The dual damascene via is etched to an underlying Cu layer 114.
In processing subsequent to the photoresist and residue removal, exposed surfaces of the dual damascene line and via, 102 and 104, are coated with a barrier layer and then the dual damascene line and via, 102 and 104, are filled with Cu.
Returning to FIG. 5, a fifth residue, which comprises the photoresist residue 42 mixed with the SiO2 etch residue 44, coats line sidewalls 116 and via sidewalls 118. A sixth residue, which comprises the photoresist residue 42 mixed with SiN etch residue 120, coats the fifth residue. A seventh residue, which comprises the photoresist residue 42 mixed with Cu etch residue 122, coats the sixth residue. The photoresist 48 remains on a second exposed surface of the second SiO2 layer 106. In the prior art, the photoresist 48, the photoresist residue 42, the SiO2 etch residue 44, the SiN etch residue 120, and the Cu etch residue 122 are removed by the plasma ashing and the stripper bath of the prior art.
Note that the fifth, sixth, and seventh residues are worst case scenarios. Depending upon a specific etch process, the fifth, sixth, or seventh residue might not be present.
Recent developments in semiconductor technology have led to proposed replacement of the second and third dielectric layers, 106 and 110, of the dual damascene structure 100 with low dielectric constant materials. Replacing the second and third dielectric layers, 106 and 110, with the low dielectric constant materials enhances an electronic device speed. Current efforts to develop the low dielectric constant materials have led to first and second categories of the low dielectric constant materials. The first category of low dielectric constant materials is a Cxe2x80x94SiO2 material in which C (carbon) lowers an SiO2 dielectric constant. The second category of dielectric materials are spinon polymers, which are highly cross-linked polymers specifically designed to provide a low dielectric constant. An example of the spin-on polymers is Dow Chemical""s SILK. SILK is a registered trademark of Dow Chemical.
Via and line geometries are progressing to smaller dimensions and larger depth to width ratios. As the via and line geometries progress to the smaller dimensions and larger depth to width ratios, the plasma ashing and the stripper bath of the prior art are becoming less effective at removal of photoresist and photoresist residue. Further, replacement of SiO2 with low dielectric constant materials raises difficulties with continued use of the plasma ashing. For the Cxe2x80x94SiO2 material, the O2 plasma attacks the C. For the Cxe2x80x94SiO2 material, the O2 plasma can be replaced with a H2 plasma but this reduces an overall effectiveness of the plasma ashing. For the spin-on polymers, especially Dow Chemical""s SILK, the plasma ashing is not a feasible method for removing the photoresist or the photoresist residue since the plasma ashing attacks the spin-on polymers.
What is needed is a more effective method of removing photoresist.
What is needed is a more effective method of removing residue.
What is needed is a more efficient method of removing photoresist.
What is needed is a more efficient method of removing residue.
What is needed is a method of removing photoresist from a substrate in which via and line geometries have small dimensions.
What is needed is a method of removing residue from a substrate in which via and line geometries have small dimensions.
What is needed is a method of removing photoresist from a substrate in which via and line geometries have large depth to width ratios.
What is needed is a method of removing residue from a substrate in which via and line geometries have large depth to width ratios.
What is needed is a method of removing photoresist from a substrate in which features are etched into a Cxe2x80x94SiO2 low dielectric constant material.
What is needed is a method of removing residue from a substrate in which features are etched into a Cxe2x80x94SiO2 low dielectric constant material.
What is needed is a method of removing photoresist from a substrate in which features are etched into a spin-on polymer low dielectric constant material.
What is needed is a method of removing residue from a substrate in which features are etched into a spin-on polymer low dielectric constant material.
The present invention is a method of removing photoresist and residue from a substrate. Typically, the photoresistxe2x80x94or the photoresist and the residue, or the residuexe2x80x94remains on the substrate following a preceding semiconductor processing step such as ion implantation or etching. The method begins by maintaining supercritical carbon dioxide, an amine, and a solvent in contact with the substrate so that the amine and the solvent at least partially dissolve the photoresist and the residue.
Preferably, the amine is a secondary amine or a tertiary amine. More preferably, the amine is the tertiary amine. Even more preferably, the amine is selected from the group consisting of 2-(methylamino)ethanol, PMDETA, triethanolamine, triethylamine, and a mixture thereof. Most preferably, the amine is selected from the group consisting of the 2-(methylamino)ethanol, the PMDETA, the triethanolamine, and a mixture thereof. Preferably, the solvent is selected from the group consisting of DMSO, EC, NMP, acetylacetone, BLO, acetic acid, DMAC, PC, and a mixture thereof.
Next, the photoresist and the residue are removed from the vicinity of the substrate. Preferably, the method continues with a rinsing step in which the substrate is rinsed in the supercritical carbon dioxide and a rinse agent. Preferably, the rinse agent is selected from the group consisting of water, alcohol, acetone, and a mixture thereof. More preferably, the rinse agent is a mixture of the alcohol and the water. Preferably, the alcohol is selected from the group consisting of isopropyl alcohol, ethanol, and other low molecular weight alcohols. More preferably, the alcohol is the ethanol.
In a first alternative embodiment, the amine and the solvent are replaced with an aqueous fluoride. In a second alternative embodiment, the solvent is added to the aqueous fluoride of the first alternative embodiment. In a third alternative embodiment, the amine is added to the aqueous fluoride and the solvent of the second alternative embodiment.